This guide is a combination of work by: the California Department of Forestry and Fire Protection, the National Arbor Day Association, and the University of California, Agriculture & Natural Resources
Finding proper care for your tree is important. Your best assurance of obtaining professional work is by using the services of an arborist Don’t Top Trees! Provided by: certified by the International Society of Arboriculture. Our City Our City Forest Forest can also provide a list of tree care companies and certified 151 West Mission Street arborists; contact us at (408) 99-TREES. For more information on how to prune young trees, San Jose, CA 95110 sign up for a Tree Amigo class or attend a pruning workshop. This guide, and all services are (408) 99-TREES provided free of cost by Our City Forest, a non-profit 501(c)3 organization. www.OurCityForest.org The type of pruning your tree gets is critical to its health, longevity, safety, and appearance. Proper pruning is Five Key Steps for Pruning Young Trees important because trees add beauty and enhance property Source: Training Young Trees for Structure & Form value, up to 27%. Improperly pruned or neglected trees can result in: suffering tree health, lessened property value, 1 Remove broken, dead, dying, diseased, or damaged increased potential hazards and liability, and increased branches. Inspect the canopy and remove or cut back these long-term maintenance costs. branches.
This guide is intended to describe how young trees 2 Select and establish a central leader. There should should be pruned. We are not encouraging tree owners only be one leader. Select the strongest and most vertical to prune large mature trees themselves. Pruning is stem as the leader and remove or cut back competing both difficult and dangerous, it’s best left to experi- stems. enced arborists. 3 Select and establish the lowest permanent branch. Reasons to Prune/Train Young Trees Look for a well-attached branch at the desired height (de- termined by location and use), and remove closely-spaced, Source: Training Young Trees for Structure & Form competing branches. The diameter of the lowest permanent Improved structural strength. By removing defects branch should be no more than one-half that of the central such as weak branch attachments and codominant stems, leader or trunk at the point of attachment. Smaller tempo- trained trees are structurally stronger than untrained trees. rary branches should be left close to the lowest permanent Structurally stronger trees have a lower potential for branch. Larger temporary branches should be pruned back failure. to three to four buds.
Reduced maintenance costs. Trained trees require less 4 Select and establish scaffold branches. Look for maintenance when they are mature. Typically, trained well-attached branches above the lowest permanent branch trees have fewer branches than untrained trees, which that are no more than one-half the diameter of the central means less pruning. In addition, well-spaced branches leader. Scaffold branches should be well spaced both verti- provide easier access for arborists, and pruning can be cally and radially. Vertical spacing should be 18 inches or accomplished in a shorter period of time. Finally, trained more for large trees and 12 inches for smaller trees. Radial trees may not have structural defects that require correc- spacing should be allowed for balanced branch distribution tion by cabling, bracing, canopy thinning, and codominant around the central leader. Leave small branches close to stem removal, which avoids substantial costs. scaffolds as temporary branches and cut back or remove larger branches. Increased tree longevity. Simply by remaining intact longer, trained trees serve as functional components of the 5 Select temporary branches below the lowest urban forest for more time than untrained trees. Trained permanent branch. Some or all the branches below the trees have a lower potential for structural failure than lowest permanent branch can be retained as temporaries. untrained trees. Failed trees and hazardous trees need to If possible, leave the smallest branches and cut back or be removed. Trees that have sustained substantial partial remove the largest branches. failure (limb or stem failure) often need to be removed because they are hazardous or unsightly. September 2006 How Much to Prune? Source: Training Young Trees for Structure & Form
Generally, no more than 25% of the canopy of a young tree should be removed in any one year (This varies for different tree species). In some cases, removing only 5 to 10% will be sufficient to develop structure and form. With particularly fast-growing trees or trees with significant defects, over 25% may need to be removed. You can reduce the height of a large tree by up to 30%. It is important that approximately 1/2 of the trees foliage originate in the lower 2/3 of the tree. Tree Location and Training
A tree’s location is an important consideration for Step 3, “Select and establish the lowest permanent branch.” The height of the lowest permanent branch is determined by both the location and use of the tree. Trees planted along streets or in parking lots need to allow clearance for vehicles. For street trees, many cities require an 8-foot (2.4 M.) clearance above the sidewalk and 14-feet (4.3 M.) over the street. Trees in parking lots need a 12 to 14-foot (3.7 to 4.3 M.) clearance. Trees in parks and yards have variable clearance requirements. If access is not needed, or if the tree is used for wind protection or as a visual screen, then the lower branches should be retained. Conifers
The Five Steps can be applied to conifers, but with some modifications. Steps 1 and 2 are important. Damaged branches and competing leaders need to be removed. Step 3 may be important depending on the tree’s location. If clearance is needed for vehicles, equipment, or people, then Step 3 should be applied. Step 4 is not as important for conifers as it is for hardwood species. In many cases this step can be skipped entirely. Look for and remove branches with weak attach- ments, however. Step 5 is needed if a lowest permanent branch is established. Field Practice
It is very important to practice the Five Steps before applying them. Review each step with a helper before making cuts. Tie string or ribbon around the leader, the lowest permanent branch, and scaffolds. Discuss reasons for your selections, and step back to look at potential impacts on tree form and size. After you are confident of your selections, then make your cuts. Again step back from time to time to assess impacts on tree form. Remember that species and conditions vary considerably, and you will always need to use good judgment. Understand the reasons for the Five Steps, and then make reasonable adjustments in the field. When to Prune?
Source: Tree City USA Bulletin #1 growth is complete. The reason for the slowing effect is that you When to prune depends to a large extent on why you reduce the total leaf surface, thereby reducing the amount of food prune. Light pruning and the removal of dead wood can manufactured and sent to the roots for their development and next be done anytime. Otherwise, here are some guidelines, but year’s growth of crown. recognizing that individual species may differ. Fall Because decay fungi spread their spores profusely in the fall and healing of wounds seems to be slower on fall Winter the most Pruning during dormancy is cuts, this is a good time to leave your pruning tools in storage. common practice. It results in a vigorous burst of new growth in the spring and should be used if that is the desired Flowering Trees If your purpose for pruning is to enhance effect. It is usually best to wait until the coldest part of winter flowering: 1. For trees or shrubs that bloom in summer or has passed. Some species, such as maple, walnut, and birches, fall on current year’s growth (e.g., crape myrtle), prune in winter. may “bleed” when sap begins to flow. This is not harmful, and 2. For trees that bloom in spring from buds on one-year-old wood will cease when the tree leafs out. (e.g., dogwood and flowering fruit trees), prune when their flowers fade. Spring At the latest, prune well before the buds swell and new leaves begin to develop. Caution: In some areas of the country, diseases or insect occurence may be affected by the time of Summer To direct the growth by slowing the branches pruning. Check with an arborist or nursery operator to you don’t want; or to slow or “dwarf” the development of a tree or branch, pruning should be done soon after seasonal see if there are any local problems. The Right Way - Where to Make The Cut
Source: Tree Pruning - Doing it Right Remove unwanted branches at their attachment point to the trunk or another branch. Shorten branches to a lower lateral branch at least 1/2 the diameter of the branch to be removed. DO NOT LEAVE STUBS. Stubs die-back and allow decay to enter the trunk or branch, This shortens the tree’s lifespan and causes potential hazards. In addition, stubs look un- natural. Making the cut: Make the cut just outside the branch bark ridge (D) and the trunk collar (E) (Figure 1). These ‘targets’ mark the boundary between the branch and the trunk. The branch bark ridge (BBR) is a raised strip of bark found on most branch crotches. When viewed from the top, it appears as D a crescent shaped ridge extending downward. From the side, it appears as a narrow triangular ridge extending downward from the crotch to the center of the trunk. It marks the upper bound- BBR ary between the branch and the trunk.
E If the BBR is not clearly visible, you can approximate its location by bisecting the crotch angle (Figure 2). Cut to lower side of this point (F) to protect the trunk or parent branch. The trunk collar generally appears as an enlarged area at the base of the branch. It’s Don’t Figure 1 actually part of the trunk (G) (Figure 2). The point at where the enlarge- Flush Basic cut ment perceptibly narrows is the lower boundary between the branch and Cut! trunk. Make your cut to the outside off this point (G) to avoid injuring the trunk. This type of cut is smaller and closes over rapidly.
F A cut made inside the BBR or trunk collar is called a ‘flush cut’ (Figure 3). The resulting wound is larger than necessary and rather injurious Figure 3 to the trunk. If the trunk collar is not obvious, the angle of the final cut G should approximate the angle that the BBR forms with the axis off the Trunk Collar limb. Angle HY should equal angle HX (Figure 4). Many tree cavities H are a result of ‘flush cuts’. Figure 2 Unobvious BBR Y X For Larger Branches: Figure 4 Make the first cut (A) on the underside of the branch about one foot from the crotch. Cut at Unobvious trunk collar least 1/3 of the branch diameter (Figure 5). Make the second cut (B) on the top side, 1 to 3 inches from the first. The limb should split away cleanly without tearing the bark or leaving a jagged edge. The remain- der can be removed with final cut (C) without damaging the tree.
Codominant Stems: On forking branches of equal or nearly equal size, (codominant stems) make the final cut just outside of the BBR to a point opposite of and perpendicular to the bottom of the BBR. To remove stem 1, cut from A to B. To remove stem 2, cut from C to D (Figure 6). Never remove both. If the BBR is not obvious, cut perpendicular to the axis of the branch to be removed. (Figure 6a). Make the cut to the outside of the mid-point of the crotch. First cut B Stem A C Stem 2 1 C A mid-point B D Final cut
Figure 5 Figure 6 Figure 6a Unobvious BBR For larger branches Codominant stems (Continued on next page) (Continued from previous page)
Source: Tree Pruning - Doing it Right To Change Leader Branches: To shorten a branch back to a lower lateral branch enough to become the leader, make the final cut outside the BBR to a point directly opposite the bottom of the BBR. You can also approxi- mate the cut by bisecting the angle formed by the BBR and an imaginary line which intersects the BBR and runs perpendicular to the axis of the trunk (Figure 7). Figure 7 Pruning for Strength
Source: Tree City USA Bulletin #1
Branch Angles and Size Narrow angles signal a point of future weakness, whether in the trunk or crown. The reason is that as the two branches grow, neither has sufficient space to add the wood needed for strength. Instead, they grow against each other. The effect is similar to hammering in a wedge. To prevent this and the expensive problems that are sure to follow, simply remove one of the two branches. For strength, the ideal branching angle approximates 10 or 2 o’clock. Lateral branches should be no more than 1/2 to 3/4 the diameter of the trunk. As the trunk grows it will strengthen the joint by adding wood around the branch - like a dowel in a chair leg. Ideal angles Rubbing Branches Branches that rub result in wounds, decay and notches. Remove one of the offending branches.
Watersprouts and Suckers These “parasite” sprouts can occur at the base or inside the crown. They Remove are rapidly growing, weakly attached, and upright. Usually they use more energy that they return to the tree. It is best to remove them as soon as possible when it is obvious they are vigorous sprouts. Rubbing Branches Lower Temporary Branches Suckers Branches below the lowest permanent branch can protect young bark from injury from the sun and add taper and strength to the trunk. Particularly in lawn plantings where lower limbs do not block passage or temp vandals, the limbs may be left for 3-4 years after planting. Then remove over the next 2-3 years, beginning with the larger temporaries. Don’t let the tem- porary branches become large and vigorous. Shorten the larger temporary branches, or remove vigorous temporaries if less vigorous ones can be selected.
Center of Gravity Young trees deformed by wind may be corrected by pruning. Move the tree’s center of gravity to a point more central over the trunk by cutting back the leader and laterals on the downward side (or direction of lean) to more Keep upright branches.
Caution: When pruning diseased trees, dip your shears in } household bleach before storing or moving to the next tree. Correcting center of Be sure to rinse and wipe dry before storage. gravity. Temporary Branches The Wrong Way - Topping Source: Training Young Trees for Structure & Form
Topping, heading-back or stubbing is an unnatural and destructive pruning technique used to reduce tree height. It is commonly practiced on trees under power lines and on many publicly and privately owned trees. People often assume that because they see it done so frequently that it is an appropriate way to prune trees. Unfortunately, few people are aware of how a tree grows, closes its wounds, and prevents the spread of disease and decay throughout itself, otherwise if would become a rare sight. WRONG: Topping
Keys to Good Pruning
Source: Tree City USA Bulletin #1
1. Prune early in the life of the tree so pruning wounds are small One-Hand and so growth goes where you want it. Pruning Shear 2. Begin your visual inspection at the top of the tree and work (secateurs) downward. 3. Don’t worry about protecting pruning cuts. Do not paint larger wounds with tree paint, the evidence is that it does not prevent or reduce decay, and actually limits healing of the wound. 4. Keep your tools sharp. One-handed pruning shears with curved blades (secateurs) work best on young trees. 5. Make safety a number one priority. For high branches use a pole pruner. Some, have both a saw and shears on the same tool. A major job on a big tree should be done by a professional arborist. Pole Pruner 6. When you prune back to the trunk or a larger limb, branches too small to have formed a collar (swollen area at base) should be cut close. (Notice in the drawing of the pruning shears that the cutting blade is cutting upward for less effort and a close cut.) Otherwise, follow the rules of good pruning of larger limbs by cutting just outside the branch ridge and collar and at a slight down-and-outward angle (so as to not injure the collar). Correct Too Too Too Do not leave a protruding stub. Pruning Close Long Slanted 7. When simply shortening a small branch, make the cut Cut at a lateral bud or another lateral branch (referred to as “head” or “headback pruning”). (See Figure 9) Favor a bud that will produce a branch that will grow in a desired direction (usually outward). The cut should be sharp and clean, and make at a slight angle about 1/4 inch beyond the bud. Figure 9 Glossary of Pruning Terms
Source: Training Young Trees for Structure & Form Lowest permanent branch. Lowest scaffold branch on tree. Canopy. See Crown. Its height is determined by tree use and location. Central leader. Dominant, upright stem that forms the main Pollard. Pruning technique by which young trees or branches trunk. are initially headed and then reheaded on an annual basis Codominant stems. Stems or trunks of approximately equal without disturbing the callus knob. size, growing at about the same rate, and attached to one another. Photosynthate. Carbohydrate produced by leaves (and other Typically, the attachment is structurally weak. chlorophyll containing tissues) during photosynthesis. Crown. Foliated portion of the tree, from the lowest branch to the Round-over. To reduce tree size by heading back all stems on tree top; synonymous with canopy. the periphery of the canopy by an equal amount. (This is not a Decurrent. Round-headed tree form; scaffold branches codomi- recommended pruning practice.) nate with central leader at maturity. Scaffold branch. A branch that is part of the main structure of Double leader. Two codominant stems growing more or less in the crown. Scaffolds arise from the central leader or main trunk. the center of the tree and jointly assuming the role of the leader. Sucker. A vigorous, upright, epicormic shoot that arises from Excurrent. Conical tree form; strong central leader is present to the latent buds below the graft union or soil level. the top of tree when mature. Leader development is dominant over Temporary branch. A branch that remains on the tree for a scaffold branch development. limited period of time. It is not part of the main structure of the Included bark. Pattern of development at branch junctions where crown. Temporaries can occur on the central leader, trunk, or bark is turned inward rather than pushed out. Synonymous with scaffold branches. embedded bark. Watersprout. A vigorous, upright shoot that arises from the Lateral. Secondary branch arising from scaffold limbs. latent or adventitious buds above the growth or graft union on Leader. See central leader. older wood.
Content Sources
This guide is a combination of work by: the California Department of Forestry and Fire Protection, the National Arbor Day Associa- tion, and the University of California, Agriculture & Natural Resources. Hagen, Bruce W. (1991). Tree Pruning - Doing it Right, California Department of Forestry Tree City USA Bulletin #1 (2000). National Arbor Day Foundation Training Young Trees for Structure and Form, Supplemental Information (2000). University of California, Agriculture & Natural Resources
For More Information
1. Take a Tree Amigo class or pruning workshop offered for free through Our City Forest: http://www.ourcityforest.org/ 2. International Society of Arboriculture: http://www.isa-arbor.com/, or http://www.treesaregood.com/ 3. City of San Jose tree permits page: http://www.sanjoseca.gov/transportation/tl_treepermits.htm 4. Registered San Jose Tree Trimming companies: http://www.ourcityforest.org/pdf/tree_trimming_companies.pdf